The present invention relates to a laser diode with a laser-active strip in a buried layer of a hetero-layer structure of III-V semiconductor material.
Laser diodes of the type having a buried active layer (buried hetero-layer) like the laser diode of the present invention are disclosed, for example, by U.S. Pat. No. 4,426,700 and by IEEE Journal of Quantum Electronics, Volume QE 15 (1979), pages 451 through 469, both incorporated herein by reference. The latter publication is involved with a discussion of the theoretical questions. The concern here is laser diodes in a semiconductor body having a hetero-layer structure. In order to achieve the lowest threshold currents, the spatial arrangement is undertaken such that the active layer, which has the form of a narrow strip also referred to as a ridge, is situated within the layer structure, i.e. is buried. This narrow strip is flanked by semiconductor material having a lower refractive index and a higher band gap. The arrangement is designed such that the supplied electrical current for generating the laser radiation is concentrated on this narrow strip and leakage currents which occur are suppressed by shunts in the proximity of the active strip. Insulating layers have been employed, on the one hand, for the suppression of such leakage currents. It is also known to employ inhibiting pn-junctions for this purpose, whereby the problem always exists that the electrical current flowing through the active strip is undesirably deteriorated. The occurrence of such influences can in fact be avoided by the topically selective growth of pn-junction layers next to the active strip. This is a very involved manufacturing method, however.
For the sake of completeness, it should be pointed out that another type of laser (gain-guided) which does not have lateral zones with lower refractive index and higher band gap is known, for example, in German OS No. 28 19 843 and in Appl. Phys. Lett., Volume 43 (1983), pages 809 through 811 as well as Volume 4 (1984), pages 1035 through 1037, all incorporated herein by reference.